Apparatus for corrective drafting of strands of discontinuous fibers



M. A. SANBORN ETAL TUS FOR CORREC March 29, 1960 APPARA STRANDS OF DISCO TIVE DRAFTING OF NTINUOUS IB Filed Oct. 28. 1955 F ERS 2 Sheets-Sheet 1 March 29, 1960 M A. sANBoRN EVAL APPARATUS FOR CORR ECTI VE DRAFTING OF STRANDS 0F DISCONTINUOUS FIBERS Flled Oct. 28. 1955 2 Sheets-Shes?I 2 THEIR ATTORNEYS United States Patent O APPARATUS non coRREcrIvn DRAFTING oF sTRANDs or DiscoNrlNUoUs FlaRs Malcolm A. Sanborn, Kingston, NX., and william G.

Klein, Newton, Mass., assignors to Bates `Manufacturing Company, a corporation of Maine Application October 28, 1955, Serial No. 543,397 1'0 claims. (ci. 19-76) -This invention relates Vto Aa system for continuously drafting strands composed of discontinuous bers by attenuation between two or more sets of draft rolls driven at diiferentspeeds, and more particularly to a system of that general organization wherein the relative speeds are induced by variable drive components controlled by sensing elements actuated by the mass or bulk of the original staand.

In the production of yarnfrom staple fibers according to conventional methods there is formed, after initial dispersion by openers and cards, an essentially continuous strand, usually called a sliver, composed of a plurality of overlapping fibers loosely but effectively held together by inter-fiber friction Vand entanglement. Since, in most cases, the weight of this initial sliver is greater than the desired weight of the iinal yarn, it is subjected to subsequent attenuating processes, as byv drafting. l'n most staple yarn production, the drafting serves a second function of increasing the straightness and parallelism of the fibers along the strand axis.

It is 'common to most textile systems that the average Weight 'of the initial slivers varies from one production u'nit to another. These slivers are also variable in weight distribution along their length. Accordingly, reduction through standard draft settings will not consistently give the desired yarn weight. Some'reduction of the gross and variable deviation from the desired weight is accomplished by combining a plurality of these initial slivers to average out these inequalities prior to reduction to desired nal weight. This combining process, known in the art as doubling is only partially successful in attaining this objective; it may, in fact, lessen the normality of the total product by adding theY characteristics of a highly yabnormal sliver to other slivers which might initially have been quite regular and normal.

This process of doubling to average out strand ab` normaliti'es has a basic disadvantage because the resulting heavier strand must receive proportionally more reduction by drafting to 4attain the desired final yarn weight. This adds both equipment and operating expense. Most important to the significance of our invention, the increased necessary drafting results in increased withinstrand variability of a short-term nature. It is well known in the textile arts that, during drafting by conventional means, there are erratic liber movements and also fairly regular drafting waves which increase the variability yof the drafted strand comparedv to the original strand. Various combinations of doubling and rte-drafting are resorted to according to the relative importance in the final product of long-term compared to Vshort-"term variations. At best, however, the resulting product is a compromise as to uniformity, the system itself being self limiting.V

It is logical `and obvious that a corrective device acting on the initial vor intermediate strands would obviate much of the objectionable result of doubling and re-drafting. Various attempts have been made in the vpast to devise such "corrective mechanisms.

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tempts, although theoretically feasible, have been commercially unsuccessful.

It has been observed that two essential elements must be present to effect significant and worthwhile corrective action on a non-uniform strand by varying the relative speed of two pairs of drafting rolls. Within the general concept of controlled variable drafting, `such that the heavier-than-desired sections are attenuated to a greater extent and the lighter to a lesser extent, it has been found that a variable speed driving system for the drafting rolls capable of responding very quickly `and sensitively to changes in the measurement'signal is essential to achieve worthwhile gains in uniformity at reasonable operating speeds. Further, it has been found that within lowinertia systems which satisfy this requirement, it is particularly important to provide means to compensate for incidental variation in drafting resistance to insure the precise drafting speed momentarily indicated for a specific degree of correction. The prior art systems either lack these elements or have attempted to introduce them by means inherently incapable of meeting the required exacting conditions.

As an example of a low-inertia variable drive, the present invention preferably utilizes an electromagnetic slip clutch, the torque output of which is governed by a control circuit. `For significant reasons, a speed control circuit of the feed-back or closed loop type has been employed, having found that the common calibrated or open loop principle is not sufciently sensitive or precise for the critical requirements of the problem. An open loop speed control system, such as, for example, a syS- tem employing a strand measuring device which alone controls the speed of a variable drive element, would be appropriate and satisfactory only if the variable drive element where both of low inertia and of such power as to practically completely over-ride or negate the effect of variations in drafting resistance. These two requirements are essentially in conflict, and from a practical standpoint are not attainable without feed-back with known equipment in a satisfactory compromise appropriate to the problem of corrective drafting of typical textile slivers or strands at economic speeds. Thus, prior art has been limited by dependence on purely calibrated control systems.

According to the present invention, a feedback voltage is generated which is directly responsive to the actual relative speed of the drafting rolls, and the feed-back lis utilized to modify the control signal for discrepancies due to drafting resistance and possible changes in characterist-ics of the driving mechanism. As is later described, this also accelerates the response. The essence of this invention is the novel and uniquely appropriate application of a feed-back control system to the important and heretofore unsolved problem of correcting weight variations in textile strands by drafting an amount proportional to the mass or bulk. v

For a complete understanding of the present invention, reference may be had to the detailed description which follows and to the accompanying drawings in which:

Fig. 1 is a schematic box-type diagram of one form of the control system of the present invention; and

Fig. 2 is a schematic perspective view of the elements comprising a particular embodiment of the present invention.

The present invention may be described in a general manner by reference to the box-type diagram represented However, these Vprior atin Fig. l of the drawings.

According to that figure, the mass of a moving sliver is measured by a sensing means v1 which detects variations 'in 'the uniformity of the mass of the Isliver, and these variations are converted by l'a transducer element 2 into a signal voltage which may,

if necessary, be amplified by a conventional unit 3 before being fed into a summation point 7 of a variable drafting system, denoted generally by the reference numeral 4.

Y The variable drafting system 4 includes a forward circuit 5 and a feed-back circuit 6. A D.C. voltage is generated in the feed-back circuit by a tachometer generator 40, which voltage is proportional to the relative speed of the drafting rolls it?, 11 (see Fig. 2.). The feed-back voltage is calibrated by the speed adjusting control 42 and converted from D.C. to A.C. by a converter 38 before being introduced to the summation point 7, at which point the feed-back voltage is subtracted from the mass signal voltage to producean error voltage. The error voltage is amplified by a phase sensitive amplifier 44 and rectified by a rectifier 8, and the error 'voltage is used to control the rotational torque applied to the draft rolls lll. For example, the error voltage may control the slip of a clutch 15, thereby, in turn, regulating the speed of the feed rolls. In this manner, the actual relative speed of the feed rolls is controlled by both the mass voltage and the speed voltage, so that changes in mass or small deviations in speed of the draft rolls produce substantial changes in error voltage to.

bring this roll speed to that dictated by the mass at any instant. Because of this action the system is capable of precise control of speed and fast response to changes in mass. Referring to Fig. 2 which illustrates a specific embodiment of the present invention, the non-uniform strand or sliver A which is to be processed to improve its uniyforrnity is passed through two sets of rolls itl and 11 suitably spaced apart and separately driven to permit attenuation of the strand A therebetween. Although the invention as described employs only two sets of rolls, any number may be provided with the relative speeds of successive pairs being regulated, if desired.

The shafts of the upper and lower rolls of the set carry meshing gears lita, 1Gb, and the rolls 1) are driven at uniform speed by a motor 12. The shafts of the upper and lower rolls of the set 11 also carry meshing gears 11a and 1lb, and the rolls 11 are adapted to be driven from a constant speed motor 13 through a transmission which includes transmission means, such as a belt drive 14, a magnetic slip clutch l5, and a shaft 16 connecting the driven element of the slip clutch with the rolls li. To provide a desired damping effect, the shaft lo is coupled to a viscous load, such as a shorted generator ll?. Alternatively, this may be accomplished electrically by a suitable kinetic damping or by an antihunt circuit. Obviously, the draft rolls 10, 11 may be driven by a single motor. The speed of the rolls 11 is varied by controlling the slip of the magnetic clutch 15. It is evident that if the peripheral linear velocity of the rolls 11 is greater than that of the rolls 1t), the portion of the strand A between the two sets of rolls will be subjected to tension which will have a drawing effect on that portion of the strand A. By increasing this drawing effect on heavier portions of the strand and by diminishing this drawing effect on lighter portions of the strand, it is possible to produce a strand of relatively uniform mass.

The detecting or sensing unit, in one preferred form, includes a guide block 20 having an open channel or slot 21 formed therein and a sensing element comprising a weighted movable tongue 22 accommodated within the channel or slot Z1 and a pivotal lever 23 supporting the tongue 22. at the free end thereof. The fixed end off the lever is suitably supported on a pin 24 in a suitable base or platform B.

The side Walls 21a and the base 21h of the channel 21 curve or taper outwardly at the entrance end, and the lower edge of the tongue 22 is curved or rounded in the direction of the moving strand to guide the strand through the channel.

As the strand or sliver A is advanced through the grooved channel or slot 21 by the action of the rolls 10, the Weight of the tongue 22 accommodated within the groove 21 compresses the strand to a substantially uniform density in order to make possible an accurate measure of the sliver mass. The tongue 22 will, of course, move in a vertical direction in response to and simultaneously with the changes in the mass of the ber bundle or strand passing beneath it, and this vertical movement is an accurate measure of the mass of this portion of the strand.

The pivotal movement of the lever 23 in response to variations in the mass of the strand displacesl the movable core Sila of a conventional linear variable differential transformer 30. The transformer 30 comprises the movable core 30a, a primary/'winding Stlb and secondary windings 3tlc. The core Sila is provided with an upwardly projecting extension 31 which carries a screwor collar 32 and a compression spring 33. The compression spring acting against a xed surface of the transformer engages the collar 32 and urges the upper end of the extension 31 in contact with the lower end of an adjustable set screw 34. In this way, any movement of the pivotal lever will shift the position of the core 30a of the transformer. Thus, when a constant A.C. voltage is impressed across the input terminals 36 of the transformer, the voltage at the output will be determined by the relative position of the'core, which position, in turn, is determined by the thickness of the compressed strand measured by the sensing element.

The output voltage of the transformer 30 may be amplified by conventional means represented by the reference numeral 37, and the amplified voltage is then applied to the input of a phase sensitive amplifier 44 in opposition to the adjusted A.C. voltage generated by a tachometer generator 4u.

rl`he tachometer generator 4t) is driven by a suitable drive transmission 41 from the shaft 16. The voltage output of the generator 4t), therefore, is proportional to the speed of operation of the rolls 11. The D.C. voltage generated by the tachometer 40 is converted to A.C. by conventional means 3S and then impressed upon the input of the phase sensitive amplifier 44 in bucking fashion to the amplified A.C. output voltage of the transformer 30. The feed-back voltage will equal the mass voltage only when the output speed is that required to maintain the proper output mass. When these two desired voltages are not equal, a differential, or error, voltage is amplified by the phase sensitive amplifier 44, rectiiied to D.C. by the rectifier 8, and then impressed across a magnetic coil 15a of the magnetic clutch. The slippage of the clutch 15 and, therefore, the speed of the rolls il is determined by the error voltage impressed across the coil 15a. v

lf, therefore, the mass of the strand measured by the sensing element is greater or less than the expected norm, the slippage of the magnetic clutch will be altered, resulting in a change in the relative speed of the rolls 10, 11.

Various other means may be employed to drive the draft rolls 11, such as a variable speed motor in combination with an amplidyne. The magnetic slip clutch 15, however, is preferred. The principal advantage of the magnetic slip clutch over a variable speed motor is that the power. required to control clutch slippage is a small fraction of that needed to drive and accelerate a motor capable of performance equal to that of a clutch. The reduced power requirement permits simpler equipment to be used for the amplifier. In order to be applicable to this problem, a magnetic slip clutch must be smooth in its action and be capable of running in continuous slip with infrequent maintenance.- Any electro-magnetically activated clutch which fulfills these requirements can be used, and the term magnetic slip clutch is used here to indicate any clutch of this general type.

One such clutch is the magnetic uid clutch recently tlcvclc-Pcd br thc. Nsticcsl urcsu cf Standards and dc: .scsibcsi is @lic NES Tcchnical. News. Bulletin, 3.7,. 5.4-60 (19.48;)Av and'3`4, 16g-,17,4 (lc/50). The driving and driven rs .0f the, clutch are immer ed in a magnetic fluid, articles suspended inoil.y When a magnetic field irnp is applied to the uid by means,y of a coil. carrying elec-.

drei@ ccmpcncnts," t lcsst with many cmmcn typcs of tentile fibers, not proportional tothe speed of drafting, )a variable torque drive will not produce proportitsallv variable src-cds with adequate stability. Thus, the viscons load"element` 1.1 coupled to. the variable speed element has. been found desirable to change the trque-to-speed .relationship by imposing a resistance which increases with increased. speed. The degree of vi ons. damping is. designed or adjusted sov that the tor,q t1etos peed'v relationship. isl reasonably constant, the feed-baci; circuit making the final minor adjustment to the,A precise speed indicated for appropriate corrective drafting. As'an example. of a. viscous load element, we have found that a shorted QC, generator is suitable andhas'any advantage in thatthe amount of load-ing can be lsily adjusted by 'varying the field excitation. A rotat-v stirrer in an oil bath isw another example. The tachometengenerator itself might be of a type to providcv a. prcpcfr viscous loading.-

vThe element d2 comprises two speed adjusting controls which2 assure that the sliver will'be attenuated tov the proper level and that a given change in mass will cause thefproper change in speed. This latter effect is called tracking.. 'Il'hve'tracking control is a voltage divider which talles. afsuitable fractionV of thev D.C. tachometer generator vbltage for use in the control so that a given change ini'speed will produce the proper-change in feedfback voltage, The other control is achieved through the ap' plication ofY a biasvoltage which sets the average speed* level.,y y

' Synchronization of thev spechic corrective drafting speed with the mass earlier measured can be effected by adjusting speed of throughputto match any delay in the response cf the. svstemrby spacing. cf thc mcasucins clcm" tY inf relation to the drafting zone, by a delay devicer in, the sensing signal system, or by any combination of the three.

DLC. to A.C. converter 3:8` comprises an electronic tube arranged in a conventional circuit to produce an AC.' voltage of a` magnitude proportional to the adjusted Ii)l lt chometer generator voltage, and of the same freque y and opposite phase as the amplified A,C- output *chase cf thc. transformers@- v The amplified outputvoltage of the transformer 30, referred tofa'sthe mass voltage, and the calibrated speed voltage generated bythe generator 40, referred to as the speed vltagefare applied to the phase sensitive amplifier 44 inf'bulcltingf manner, sothat the actual input to be ampliiid is. the"dii erencer of the two. The difference or error voltage is` in p hasewith either the mass voltage or Ithe speed voltage, whichever is. larger.

The phase sensitive amplifier 44 is of conventional design. With the errori-voltageequal to zero there is still a D.C. outputvoltage called. the. zero signal output. This D C. voltage causes a certain voltage to be applied to clutch, called the nullvoltage. When ythe mass voltagedominates the speedvoltage, the D.C.V clutchrvotage,

andl vthev speed, is increasedy and,4 when the speed 7 5 voltage dominates, the D.C. clutch voltage and speed are tlccrcascd- `r'lfhere are, of course, alternative arrangements which may be used within the limits of the invention described in theY claims. The rolls 10 rather than the rolls 11 may be driven at variable speed. Two or more sets of rolls may be used and more than one set can be driven at variable speeds. It may be desirable, in order to guard against making a product of improper mass when the prime movers' speed varies, to use two tachometers, utilizing the difference of the two voltages for control puEPOses.

Any mass measuring device which reliably produces a signal proportional to mass may be used. Capacitances and photoelectric devices, such as those used on textile. liber uniformity measuring devices, are alternatives which may be used in place ofthe tongue and groove device shown in Eig. 2.` As a further modification, we have achieved satisfactory results using a D.C. amplifier as well as` with an'A.C. amplifier in place of the phase sensitive amplifier now employed. As discussed before, any form of viscous load which is adequate may be used, and, under certain circumstances, no viscous load may be necessary. It may be omitted without altering the essential principles of the invention.

While we have shown specific systems, by Way of example, it is understood that the invention is not to be .limited to. any specified form or embodiment except insofar as such limitations are set forth in the claims which follow.

We claim:

1. Apparatus for corrective drafting of strands made. from discontinuous fibers comprising pairs of draft rolls, the. strand travelling from one pair to the next, means formeasuring thev mass of the strand comprising a res stricted passage through which the strand is guidedr Weighted means movable within said restricted passage. for compressing theV strand to substantially a uniform density, avariable speed drive for at least one of the. pairsof draft rolls, means controlledr by the movement of the weighted means for regulating the speed of the drive, means for generating. a voltage the value of which is a function of the, relative speed of the two pairs of rolls, and` means forimpressing said generated voltage as a feedbackV control for said variable speed drive to further insure'the operation of the variable speed drive system at the speed dictatedv by the mass measurement, thereby drafting the strand between the pairs of draft rolls the` amount," indicated by the measured mass to produce a strand of improved uniformity.

2.. Apparatus. for corrective drafting of strands madeI fromA discontinuous fibers comprising means for detect-- ing the uniformity of a moving fiber strand, first and second sets of draft rolls, the strand travelling from one set of draft rolls to the other in succession, means for driving at least one of said sets of draft rolls through a, drive transmission which includes a magnetically controlled slip clutch, the slip of said clutch determining the relative velocity of the two sets of rolls, thereby 'cone trolling the degree of attenuation of the strand between the two sets of draft rolls, an electrical circuit for con-v trolling the slippage of the clutch, a generator driven at a speed'which varies as the relative speed of the draft rolls, the generated voltage being impressed upon said electrical circuit, and transducer means controlled by the detecting means for producing a variable voltage determined by the mass of the strand sensed by the detecting means, said voltage being impressed on the electrical circuit opposing said generated voltage, the resulting liow of current in said electrical circuit determining the relative velocity of saidl sets of rolls. c A

3. Apparatus for corrective drafting of strands madeY from discontinuous fibers comprising first and second. sets of draft rolls, the strand travelling from one set of` draft rolls'to the other in succession, means for driving? 7 -one of said sets of rolls at a constant speed, means for driving the other of said sets Vof rolls through a `drive transmission which includes a magnetically operated slip clutch, the degree of slip of said clutch determining the speed of the rolls driven thereby, a channel forming a narrow passageway through which the strand Yis fed in an axial direction, a pivoted lever, a weighted tongue carried by said pivoted lever, said tongue engaging the moving strand within the channel and compressing it to a relatively uniform density, the pivotal movements of the lever being a measure of the variations in the uniformity of the strand, a transducer having a movable core, the position of the core of said transducer being determined by the pivotal movements of said lever, and an electrical circuit to transmit the variations in the output voltage of the transducer to the magnetically controlled slip clutch to alter the speed of the rolls driven thereby in Yaccordance with the degree of attenuation desired on the'portion of the strand between the two sets of rolls.

4. Apparatus as set forth in claim 3 including a generator driven by the variable speed rolls, the output volt-v age of said generator being proportional to the relative speed of the draft rolls and being impressed on said electrical circuit in bucking fashion to the output voltage of the transducer, the summation of the two voltages serving to control the magnetically controlled slip clutch.

5. Apparatus for corrective drafting of strands madel from discontinuous fibers comprising means for detecting the uniformity of a moving iber strand, n`rst and second sets of draft rolls, the strand travelling from one set of draft rolls to the other in succession, means for driving at least one of said sets of draft rolls through a drive transmission which includes a magnetically controlled slip clutch, the slip of said clutch determining the relative velocity of the two sets of rolls, thereby controlling tlie degree of attenuation of the strand between the two sets of draft rolls, an electrical circuit for controlling the slippage of the clutch, a generator driven at a speed which varies as the relative speed of the draft rolls, the generated voltage being impressed upon said electrical circuit, transducer means controlled by the detecting means for producing a variable voltage determined by the mass of the strand sensed by the detecting means, said voltage being impressed on the electrical circuit opposing said generated voltage, and voltage control means for regulating at least one of the voltages impressed on said electrical circuit, providing a predetermined relationship between the relative speeds of the draft rolls and the mass of the portion of the strand being attenuated, the flow of current in said electrical circuit resulting from deviation from this predetermined relationship, said current causing the relative speed of the draft rolls to change and establish the said relationship.

6. Apparatus for corrective drafting of strands made from discontinuous fibers comprising at least two sets of draft rolls, the strand traveling from one set to the next for attenuation therebetween, a variable speed drive for at least one of the sets of draft rolls, a signal summating circuit, the output of which regulates the variable speed drive, means for measuring the mass of the strand, means for converting the measurement of the mass of the strand into an electrical input impressed on said signal summatingcircuit, means for generating a voltage the value of which is determined by the actual relative speed Vof the sets of draft rolls, and means for impressing said voltage on said signal summating circuit.

7. Apparatus for corrective drafting of strands made from discontinuous fibers comprising at least two sets of draft rolls, the strand traveling from one set to the next for attenuation therebetween, a variable speed drive for at least one of the sets of draft rolls, an electrical circuit for regulating the variable speed drive, means for measuring the massof the strand, means for converting the measurement of the mass of the strand into v.a-voltage input impressed on said ,electrical circuit, means for generating va voltage, the value of which is determined by the ,actual relative speed of the sets of draft rolls,.and means for impressing the generated voltage on said electricalV circuit to compensate for any discrepancy between the relative speed of the draft rolls necessary to afford Vthe desired attenuation and the actual relative speed of the draft rolls, the said electrical circuit serving as a sum mating circuit for the different voltages impressed thereon.

8. Apparatus for corrective drafting of strands made from discontinuous fibers comprising at least two pairs of draft rolls, the strand travelling from one pair to the other in succession, means for measuring the mass of the strand, a variable speed drive for at least one of the pairs of draft rolls, means controlled by the means for measuring the mass of the strand for regulating the speed of the drive, means for generating a voltage the value of which is a function of the relative speed of the two pairs of rolls, and means for impressing the generated voltage as a feed-back control on said variable speed drive to insure the operation of the variable speed drive at the speed dictated by the mass measurement, thereby drafting the strand between the pairs of draft rolls by the amount indicated by the measured mass to produce a strand of improved uniformity.

, 9. Apparatus for corrective drafting of strands made from discontinuous bers comprising first and second sets of draft rolls, the strand travelling from one set of draft rolls to the other in succession, drive means for said first and second sets of draft rolls, a magnetically controlled slip clutch for transmitting the drive to at least one of said sets of rolls, the degree of slip of the clutch determining the relative speed of rotation of the two sets of rolls, an electrical circuit for impressing a'pre'determined voltage on said magnetically controlled slip clutch to control the degree of slip thereof, the torque transmitted by the clutch varying directly with the voltage impressed thereon, means to detect variations in the uniformity of the strand, transducer means for translating the variations in uniformity into variations in the voltage impressed on the magnetically controlled clutch, means for generating a voltage the value of which is a function of the relative speed of the two sets of rolls, and means forY impressing the generated voltage as a feedback control on said magnetically controlled slip clutch to insure the operation of the magnetically controlled slip clutch at the speed dictated by the variation in uniformity, thereby drafting the strand between the sets of draft rolls by the amount indicated by the means to detect variations in the uniformity of the strand to produce a strand of improved uniformity. t

10. Apparatus for corrective drafting of strands rmade from discontinuous fibers comprising at least twofpairs of draft rolls, the strand traveling from one pair of draft' Y rolls to the other in succession, detecting means to measure variations in the uniformity of the strand, a variable speed drive for at least one of the pairs of draftrolls,

means controlled bythe detecting means for regulating the variable speed drive to change the relative speeds of v, rotation of the two pairs of draft rolls, means for generate ing a voltage the value of which is a function ofthe relative speeds of rotation of the two pairs of draft rolls, and means for impressing the generated voltage as a fee dback control on said means controlled by the detectingA means to insure the operation of the variable speed drive at the speed dictated by the detecting means, thereby drafting the strand between the pairs of draft rolls by the amount indicated by the detecting means to produce a strand'of improved uniformity.

References Cited in the file of this patent` UNITED STATES PATENTS 2,407,100 I Richardson Sept. 3, 1946 2,648,502 Y Trofimov Aug. 11,1953 2,682,144 Hare June 29, 1954 2,812,553 Coulliette Nov. 12, 1957 

